Aircraft need to produce varying levels of lift for take-off, landing and cruise. A combination of wing leading and trailing edge devices are used to control the wing coefficient of lift. The leading edge device is known as a slat. On larger aircraft there may be several slats spaced along the wing edge. During normal flight the slats are retracted against the leading edge of the wing. However, during take-off and landing they are deployed forwardly of the wing so as to vary the airflow across and under the wing surfaces. The slats usually follow an arcuate or curved path between their stowed and deployed positions. By varying the extent to which the slat is deployed along said path, the lift provided by the wing can be controlled.
An assembly is required to support and guide movement of a slat between stowed and deployed positions and a typical arrangement showing a cross-section through part of a wing 1 and a slat 2 in its stowed position is illustrated in FIG. 1. As can be seen from FIG. 1, the slat 2 has an arcuate support arm or slat track 3, one end 4 of which is rigidly attached to the rear of the slat 2 and extends into the wing 1.
The slat track 3 penetrates machined rib 5 and wing spar 6 forming the wing structure. The slat track 3 defines an arc having an axis and is mounted within the wing so that it can rotate about that axis (in the direction indicated by arrows “A” and “B” in FIG. 1) to deploy and retract the slat 2 attached to one end of the slat track 3.
To drive the slat rack 3 so as to deploy or retract the slat 2, a toothed slat rack 7 having an arcuate shape corresponding to the arcuate shape of the slat track 3 is mounted within a recess 3a on the slat track 3 and a correspondingly toothed drive pinion 8 is in engagement with the teeth 7a on the slat rack 7 so that when the drive pinion 8 rotates, the teeth 8a on the drive pinion 8 and the teeth 7a on the rack 7 cooperate to pivot or drive the slat rack 7 and the slat attached thereto, into a deployed position, i.e. in the direction of arrow “A” in FIG. 1. Typically, the slat track 3 rotates through an angle of 27 degrees between its fully stowed and fully deployed positions. Rotation of the pinion 8 in the opposite direction also drives the slat track 3, in the direction of arrow “B”, back into its stowed position, as shown in FIG. 1.
The drive pinion 8 is mounted on a shaft 9 that extends along, and within, the leading edge of the wing 1. Several gears 8 may be rotatably mounted on the shaft 8, one for driving each slat 2 so that when the shaft 9 is rotated by a slat deployment motor close to the inboard end of the wing 1, the slats are all deployed together.
The slat track 3 has a generally square cross-sectional profile such that its upper and lower surfaces 3b, 3c each define a portion of a curved surface of a cylinder each having its axis coaxial with the axis of rotation of the slat track 3. The slat track 3 has an arcuate mid-line, indicated by X-X in FIG. 1, that extends through the centre of the slat track 3 parallel to and equally spaced from each of its upper and lower surfaces 3b, 3c which defines the path along which the slat track 3 travels.
The slat track 3 is supported between roller bearings 10a, 10b both above and below the slat track 3 and the axis of rotation of each bearing 10a, 10b is parallel to the axis of rotation of each of the other bearings 10a, 10b and to the axis about which the slat track 3 rotates in the direction of arrows “A” and “B” between its stowed and deployed positions. The upper bearings 10a lie in contact with an upper bearing track 3b of the slat track 3 and the lower bearings 10b lie in contact with a lower bearing track 3c so that they support the slat track 3 and guide it during deployment and retraction. The bearings 10a, 10b resist vertical loads applied to the slat 2 during flight both in stowed and deployed positions and also guide movement of the slat track 2 during slat deployment and retraction.
It will be appreciated that the bearings 10a, 10b resist loads that are applied in the vertical direction only. By vertical loads are meant loads that act in a direction extending in the plane of the drawing or, in the direction that acts at right-angles to the axis of rotation of each bearing.
It will be appreciated that there can be significant side loads acting on a slat 2 in addition to loads acting in a vertical direction during flight, especially as the slats 2 generally do not extend along the leading edge of the wing 1 exactly square to the direction of airflow. By side-loads is meant loads that act in a direction other than in a direction that extends in the plane of the drawing or, in other words, those loads that act in a direction other than at right-angles to the rotational axis of each bearing 10a, 10b. 
To counteract side-loads, it is common to support the slat track 3 by further bearings 11 disposed on either side of the slat track 3 as opposed to the vertical load bearings 10 mounted above and below the slat track 3. These side-load bearings 11 may not be rotational and may just comprise bearing surfaces, pads or cushions against which the side walls of the slat track 3 may bear when side loads are applied to the slat 2.
It will be appreciated that space for components within the wing structure close to the leading edge of the wing 1 is very limited, especially once the slat track 3 together with its vertical and side load bearings 10a, 10b, 11, and the drive pinion 8 have all been installed. The requirement to house all these components places considerable design restrictions on the shape of the wing 1 in addition to increasing weight, manufacturing costs and complexities.
As the additional side-load bearings 11 are disposed between each of the upper and lower bearings 10a, 10b, these bearings must be spaced from each other in the circumferential direction about the axis of the slat track 3 by a distance which provides sufficient space between the bearings 10a, 10b to receive the side-load bearings 10a, 10b. As a consequence of this, a further disadvantage with the conventional assembly is that the slat track 3 must be relatively long to accommodate the desired maximum deployment angle for the slat 2 whilst ensuring that the slat track 3 is adequately supported by two vertical load bearings 10a above the slat track 3 and two vertical load bearings 10b below the slat track 3, even at maximum deployment. As a result of its extended length, the slat track 3 penetrates the spar 6 and so the free end of the slat track 3 must be received within a track can 13 to separate the slat track 3 from the fuel stored within the wing 1 behind the spar 6. However, it is undesirable to have openings in the spar 6. It will also be appreciated that the requirement for a track can 13 also presents additional problems and assembly issues with the need to provide an adequate seal where the track can 13 is attached to the spar 6.
The Applicant has developed a slat support assembly that substantially overcomes or alleviates the issues identified above and which is described in detail in WO2010/026410, which is incorporated herein in its entirety.
WO2010/026410 discloses a slat support assembly in which at least some of the bearing tracks of the slat support arm and the associated bearings are configured so that each bearing counteracts load applied to the slat support arm in more than one direction. More specifically, the slat support arm may have a pair of adjacent upper bearing surfaces which are arranged at an angle relative to each other so that a bearing associated with one upper bearing track on the slat support arm does not share a common axis with the bearing associated with the other upper bearing track on the slat support arm. Furthermore, the slat support arm may have a pair of adjacent lower bearing tracks that are arranged at an angle relative to each other so that a bearing associated with one lower bearing track does not share a common axis with the bearing associated with the other lower bearing track. Alternatively, the lower bearings may be arranged with their axes coaxial so it is only the upper bearings whose axes are angled relative to each other.
For convenience and ease of assembly, the bearings are mounted in one or more bearing blocks each of which are attachable between ribs of the aircraft wing to retain the bearing block in position. Each bearing block is provided with an opening through which the slat support arm passes, together with four cavities that surround the opening each of which receives and mounts a bearing within the block so that each bearing has its bearing surface in rolling contact with its associated bearing track on the slat support arm that extends through the opening.
The above-described arrangement provides an assembly in which each of the bearings is able to withstand loads applied to the slat support arm in multiple directions, so additional side-load bearings or cushions are no longer required.
Thus, more space is provided within the leading edge of the wing that enables bearings to be positioned closer together in the deployment direction and allowing a shorter slat support arm to be used than is usual.
Whilst the slat support assembly known from WO2010/026410 offers a number of advantages, the present invention seeks to provide modifications that enable a degree of adjustment during assembly of the slat support assembly to compensate for, for example, manufacturing tolerances and/or to enable a pre-load to be applied between the track and the bearings.